Etching of aluminum

ABSTRACT

An etchant liquid for metals (which consist mainly of aluminum) comprising an aqueous sulfuric acid solution containing halogen ions and the ions of a metal having an ionization tendency less than that of aluminum. An etching bath containing the above liquid also comprising a water-immiscible organic liquid, and a surface active agent prepared by the phosphoric esterification of a polyalkylene glycol having alkylene oxide linked with the hydrocarbon residual group thereof. A process for forming a photographic image of an acid-resistant coating applied to the surface of a metallic plate (which consists mainly of aluminum) which comprises etching the plate using the described etchant liquid or etching bath.

United States Patent Gohein Marukawa Takashi Oikawa, Tokyo; RyotatsuOtsuka, Tokyo; Naomi Kagaya, Kawasaki-shi, all of [72] Inventors 32Priority Dec. 13, 1967, Sept. 7, 1968, Sept. 27, 1968,

Nov. 6, 1968 [33] Japan [31] 42/79542, 43/64051, 43/69420, and 43/80626[54] ETCHING OF ALUMINUM 8 Claims, No Drawings [52] US. Cl 156/22,156/14, 252/794 [51] Int. Cl C23i 1/00, B44c l/22,C23g H22 [50] Field ofSearch l56/22, 23,

[ 56] References Cited OTHER REFERENCES Chemical Abstracts" Vol. 67,1967 Article 24659f on Chemical Polishing of Aluminum.

Primary Examiner-Jacob H. Steinberg Attorney-Sughrue, Rothwell, Mion,Zinn & Macpeak ABSTRACT: An etchant liquid for metals (which consistmainly of aluminum) comprising an aqueous sulfuric acid solutioncontaining halogen ions and] the ions of a metal having an ionizationtendency less than that of aluminum.

An etching bath containing the above liquid also comprising awater-immiscible organic liquid, and a surface active agent prepared bythe phosphoric esterification of a polyalkylene glycol having alkyleneoxide linked with the hydrocarbon residual group thereof.

A prdcess for forming a photographic image of an acidresistant coatingapplied to the surface of a metallic plate (which consists mainly ofaluminum) which comprises etching the plate using the described etchantliquid or etching bath.

ETCIIING F ALUMINUM BACKGROUND OF THE INVENTION I. Field of theInvention The present invention relates to the etching of metallicplates consisting primarily of aluminum.

2. Description of the Prior Art There have hitherto been developedvarious etching methods for processing magnesium, zinc, copper, oralloys thereof, but there has never been proposed a practical corrodingor etching method for metallic plates mainly consisting of aluminumwhich is inexpensive in comparison to processes for etching plates madeof magnesium, zinc or alloys thereof. This is surprising since aluminumis light in weight when compared with a zinc plate or copper plate ofthe same thickness. Thus, the handling of an aluminum plate is easier.

In addition, the etching of metallic plates mainly consisting ofaluminum in accordance with this invention is rapid, about -20 percentfaster, in comparison to processes for etching plates made of magnesium,zinc or alloys thereof.

As materials for rapidly etchant metals mainly consisting of aluminum,there are the acids, such as hydrochloric acid, hydrofluoric acid,phosphoric acid and the like; and alkalis, such as sodium hydroxide.However, the surface of metals mainly consisting of aluminum which havebeen etched by such materials are very rough. Thus, such materials areunsuitable for use as an etching bath. An etching bath is required tohave the following properties: it must etch the metal rapidly; theresist must not be damaged at the etching site; the relief which isformed must not be side-etched; and the cor roded or etched surface mustbe smooth. Moreover, it is desirable, if possible, that theconcentration of the etchant liquid be low and that the etchant liquidnot generate harmful gases during etching. The present invention amplymeets all of the requirements of the art.

The present invention provides a photoengraving process, a method ofmanufacturing name plates and metallic patterns or the like, by using asthe printing plate a metal mainly consisting of aluminum.

SUMMARY OF THE INVENTION An etchant liquid for metals which consistmainly of aluminum is provided comprising an aqueous sulfuric acidsolution containing halogen ions and the ions of a metal having anionization tendency less than that of aluminum.

An etching bath for metals which consist mainly of aluminum is providedbasically comprising the above liquid and also containing awater-immiscible organic liquid, and a surface active agent prepared bythe phosphoric-esterification of a polyalkylene glycol having alkyleneoxide linked with the hydrocarbon residual group thereof.

A process for corroding or etching a photographic image of an acidresistant coating which has been applied to the surface of a metallicplate which consists mainly of aluminum is also provided comprisingetching utilizing either the above described etchant liquid or etchingbath.

As an optional embodiment, nitrate ion (N0 may be present in the etchingbath or the corroding liquid.

An object of the present invention is to provide a etchant liquid forrapidly and uniformly etching a photographic image of an acid resistantcoating on the surface of a metal which mainly consists of aluminum.

Still another object of the present invention is to provide metals whichmainly consist of aluminum and which can suitably be used in the etchingprocess of this invention.

A still further object of this invention is to provide articles of ametal mainly consisting of aluminum prepared by the etching process ofthis invention.

These and further additional objects of this invention can be attainedby the present invention, which will be explained in further detail bythe material which follows:

DESCRIPTION OF THE PREFERRED EMBODIMENTS The most preferred metal usedin the present invention is a metal consisting essentially of Al, i.e.,A1 metal per se, consisting of more than 97 percent by weight Al andunavoidable impurities, or an Al-base alloy containing Zn or Zn and Sn.

When these metals are etched with a etchant liquid, the metals have asmooth and beautiful surface. In addition, the metals have theproperties set out in the following paragraphs.

The smoothness of the surface of the Al-base metal or alloy consistingof more than 97 percent by weight Al when etched by a etchant liquid ofthe present invention, shows increased smoothness. In addition, theetching speed of the etchant liquid of the present invention isincreased as the purity of the metal (proportion of Al) is increased.Accordingly, AI base metal having a purity of greater than 99 percent byweight is preferable in the present invention. On the other hand, if thepurity of the Al used becomes less than 97 percent by weight, problemsoccur, such as that the Al-plate will crack during working, which makesthe etched surface unacceptable.

An Al-base alloy having incorporated therein from about 0.5 to about 10percent by weight Zn, or an Al-base alloy having incorporated thereinfrom about 0 .5 to about 10 percent by weight Zn and from about 0.04 toabout 2 percent by weight Sn will be more rapidly etched than theaforesaid Albase metal or alloy. In addition, the etched surface of thealloy will be smooth and uniform, and the fabricability of the alloyinto shaped articles, such as plates, will not be harmed by etching.

To further define the aluminum purity which is required in the metalsand alloys processed in the present invention, when an aluminum alloy isutilized, the amount of aluminum contained therein should be more thanpercent. However, in the case of an aluminum metal" (not an alloy), theamount of aluminum contained therein should be greater than 97 percent.The amount of materials which remain are, essentially, unavoidableimpurities.

One embodiment of this invention is an etchant liquid for consistingessentially of aluminum and comprising an aqueous sulfuric acid solutioncontaining the ions of at least one halogen and the ions of at least onemetal having an ionization tendency which is less than that of aluminum.In another embodiment of this invention, the etchant liquid is anaqueous sulfuric acid solution containing the ions of at least onehalogen and N0 together with the ions of at least one metal having anionization tendency less than that of aluminum. Unless otherwiseindicated in this description, parts means parts by weight."

The ions of any metal having an ionization tendency less than that ofaluminum (hereinafter often referred to as an LI. metal, which is torepresent low ionization"), may be incorporated in the aforesaid etchantliquid of this invention but Cu, Fe, Ni, Co, Sn and Zn are preferred,with Cu, Fe, and Ni being most preferred.

To incorporate the ions of the metal with a reduced ionization tendencyin an aqueous sulfuric acid solution, there is added thereto a compoundof the metal which is capable of being dissolved, in the aqueoussolution to dissociate the metallic ions therein, such as a halogencompound, such as chloride, a nitrate, a sulfate, a phosphate, ahydroxide, or an oxide of the metal. In addition, the Li. metallic ionsmay be formed in an aqueous sulfuric acid solution by dissolving themetal directly in the aqueous solution, instead of adding the aforesaidmetallic compound.

The halogen ions, namely, Cl, F, Br and I, may all be incorporated intothe aforesaid etchant liquid of this invention, but C1 and F arepreferred.

To provide the halogen ions in the aqueous sulfuric acid solution, theLi. metal may be added to the aqueous sulfuric acid solution as a saltof halogen, preferably the chloride or fluoride salt; or a hydrogenhalide, preferably hydrochloric acid or hydrofluoric acid may be addedto the system separately from the addition of the aforesaid L.l.metallic ions.

To provide the No in the aqueous sulfuric acid solution, the aforesaidL.l. metal may be added to the aqueous sulfuric acid solution as anitrate of the metal, or nitric acid may be added to the system.

The concentration of the sulfuric acid in the etchant liquid of thisinvention generally is about 3 to about 20 percent by weight, preferablyabout to about percent by weight. If the sulfuric acid concentration islower than about 3 percent by weight, the etching power of the liquid isweak, while if the concentration thereof is greater than about percentby weight, the etching action is too violent, and the relief which ismade by etching a photographic image of an acid-resistant coating on thesurface of the metallic plate will be side-etched during the etchingoperation.

The concentration of the L.[. metallic ions in the etchant liquid isusually about 0.004 to about 2.0 gram-ions/liter, preferably about 0.01to about 1.0 gram-ions/liter. If the concentration of the LL metallicions is lower than about 0.004 gram-ions/liter, there is no accelerationof the etching rate by the ions of the L1. metal, while if theconcentration thereof is greater than about 2.0 gram-ions/liter, therelief will be violently side-etched.

The concentration of the halogen ions is usually about 0.1 to about 7.0gram-ions/liter, preferably about 0.15 to about 5.0 gram-ions/liter. Ifthe concentration of the halogen ions is lower than about 0.1gram-ions/liter, the rate of etching will not be increased too greatly,and will not become violent, while if the halogen concentration isgreater than about 7.0 gram-ions/liter, the surface of the etched areasbecome very rough.

The concentration of the NO is usually lower than about 2gram-ions/liter but preferably less than about 1 gramions/liter. 1f theconcentration of the ion is higher than about 2 gram-ions/liter, theetched surface of a metal mainly consisting of aluminum will becomepassive, which reduces the etching speed.

When a metal mainly consisting of aluminum (hereinafter referred to bythe abbreviated phrase Al metal") is etched in an aqueous solution about3-20 percent by weight sulfuric acid solution at room temperature, theetching rate is very low. ln contrast to this, when the Al metal isetched in the etchant liquid of this invention, that is, an aqueoussulfuric acid solution of about 3-20 percent by weight, containinghalogen ions and the ions of a metal having an ionization tendency lessthan that of aluminum at room temperature, the etching speed is greatlyincreased, without any roughening of the etched surface of the metal.Moreover, when NO is further added to the etchant liquid containing theaforesaid halogen ions and the L.l." metal ions, the etching rate iseven further increased.

The following nonlimiting theory is offered to explain the unexpectedresults obtained upon the practice of the present invention.

It is believed that when the surface of a metallic plate mainlyconsisting of aluminum is treated with the etchant liquid of thisinvention, the ions of the metal having an ionization tendency less thanthat of aluminum which are etching in the liquid are replaced withaluminum to cause the reaction:

A] A1 +3 e whereby the replaced metal is deposited on the etched surfaceof the metal. A similar viewpoint is that the etching reaction occurswhen the metal ion is reduced as, for example, in the following formula:

Fe +e Fe Thus, in any reaction, the metal ions in the etchant liquidpromote the etching of the metal mainly consisting of aluminum. Also,when the halogen ion or the halogen ions and the NO 'are added to anaqueous sulfuric acid solution containing the, ions of the metal havingan ionization tendency less than that of aluminum, the etching rate ofthe metal mainly consisting of aluminum is further increased by theinteraction between 13*, S0,, the metal ions, the halogen ions and theNO 'ions. This interaction is a specific one that does not occur in thecase where a metal mainly consisting of aluminum is treated only with anaqueous sulfuric acid solution or an aqueous sulfuric acid solutioncontaining only the ions of the aforesaid L.l." metal. 1

In the following table, the results of etching tests are shown whereinvarious etchant liquids consisting of aqueous sulfuric acid solutionscontaining various ions are utilized to treat metals mainly consistingof aluminum.

1n the test, ml. of the etchant liquid is charged in a 200 ml. beaker,and while maintaining the temperature of the beaker at 24 C. i 1 C.,various test pieces (20X40Xl mm.') are immersed in the etchant liquidfor 15 minutes, the etched depth of the metal then being measured.

In the following table, percent means percent by weight. For instance,in experiment No. 11, the iron recited therein will be dissolved in amixed solution of sulfuric acid and hydrochloric acid to form FeCl andFe,(SO,) in the liquid. It is believed that the moieties formed in theionized solutions under consideration will be self-apparent to oneskilled in the art.

TABLE I Tabulation of Etching Data on Metals Mainly Consisting of Al No,Composition of Depth of etchant Composition of Corrosion liquid (byweight) Metal (by weight) (mm.)

1. H 80, 10% Zn 1%, slight 0 'impulily level Bal. water balance AI 2, H50, 10%, "CI 1.0% Zn 1%, slight O impurity level Hal. Water balance Al3.11, so, 10%,HF1.0% Zn 1%, slight 0 impurity level Bal. water balanceA1 4.11,,so,10%,c11so,

1.0% Zn 1%, slight 0 impurity level lial. water balance A1 5111,80,10%,CuCl

1.0% Zn 1%, slight 0.12

impurity level Bal. water balance Al 011,50, 10%,cuc1,

l.0% Zn 1%, slight 0.30

impurity level HCl 3.0%, bal. water balance A1 7. 11,so, 10%, 0150,

1.0% Zn 1%, slight 0.33

impurity level HF 3.0%, Hal. water balance Al s.11,so,10%,cuc1,

1.0%, Zn 1%, slight 0.67

impurity level HCl 3.0%, HNO 1.0% balance Al Bal. water 911,50, 10%,011040,

1.3% Zn 1%, slight 0.55

impurity level NaF 3.0%, Bal. water balance A1 10.H,S0, 10%, FeCl 2.0%Zn 1%, slight 0.31

impurity level HCl 5.0%, Bal. water balance Al 11.11,so,11.2%,11c1

6.4% Zn 1%, slight 0.25

impurity level Fe powder 08%, Bal. water balance Al 12. H,SO,10%, NiCl,

0.5% Zn 1%, slight 0.48

impurity level (30040, 1.0%,13111. water balance Al 13.11,so,10%,1-11c1,

0.5% Zn 1%, slight 0.48

impurity level 011010, 0.9%, net 0.6% balance Al Bal. water 14.14 50,l0%, NiCl,

1.0% Zn 1%, slight 0.37

Table l Continued impurity level CuSO, HCl 0.6%, balance Al Bal. water15. 11,80, 10%, Cu(N0 1.0% Zn 1%, slight 0.42

impurity level HCl 3.0%, Bel. water balance Al 16. 11,80, 10%, CoCl 1.0%Zn 1%, slight 0.52

impurity level CuCl, 0.5%, HCl 2.0%, balance A1 Bal, water 17. n,so,10%, 21101,

2.0% Zn 1%, slight 0.30

im urity levcl CuCl, 0.5%, HCl 2.0%, balance A1 Bal, water lll. H,so,10%, sncl,

2.0%, Zn 1%,slight 0.25

impurity level NiCl 1.0%, CI 2.0%, balance Al Bal. water 19. H,SO 10%,NiCl,

045%, A1. 99.2% of 0.20 Cu(NO 0.9%, "CI 0.6% rest impurity 2011,80,10%,N1C1,

0.5%, Zn 2%, rest 0.55 Cu(NO 03%, HCl 0.6% impurity and Al 21. H,S0 10%,MC],

0.5%, Zn 1%, Sn 0.2%, 0.80 Cu(NO,), 0.9%, HCl 0.6% rest impurity and Al22. H,SO 10%, HBr 3.5% Zn 1%, unavoidable 0.l4

Cu(NO,,) 1.0%, Bal. water impurity, bal Al 23. H,S0, 11%, Hl3.5% 0.11

Cu(N0 1.0%, bal. water According to another embodiment of the presentinvention, there is provided an etching bath for a metal mainlyconsisting of aluminum which comprises an aqueous sulfuric acid solutioncontaining the ions of at least one metal having an ionization tendencyless than that of aluminum, the ions of at least one halogen, awater-immiscible organic liquid, and a surface active agent prepared bythe phosphoric-esterification of a condensed alkylene oxide-typenonionic surface active agent.

Further, according to still another embodiment of the present invention,there is proposed an etching bath for a metal mainly consisting ofaluminum which comprises an aqueous sulfuric acid solution containingthe ions of at least one metal having an ionization tendency less thanthat of aluminum, the ions of at least one halogen, N0 awater-immiscible organic liquid, and a surface active agent prepared bythe phosphoric-esterification of a condensed alkylene oxidetype nonionicsurface active agent.

In the above two embodiments, the types, the amounts added to theetching bath, the metal mainly consisting of aluminum, sulfuric acid,the ions of at least one metal having an ionization tendency less thanthat of aluminum, and the ions of at least one halogen" have the samemeanings as explained in the aforesaid portion of the applicationrelating to the etchant liquid of the present invention.

The water-immiscible organic liquid employed in the present inventionmay be illustrated by compounds such as aromatic, aliphatic, andnaphthenic hydrocarbons having a boiling point higher than 80 C., suchas ligroin, kerosene, gas oils, hydrocarbon type lubricating oils,aromatic solvents (for example, Solvesso No. 100 and No. 150, trade nameof the Esso Standard Oil Co.), terpene, liquid paraffin, etc.;chlorinated hydrocarbons such as liquid chlorinated paraffin,chlorodiphenyl, etc.; unsaturated higher aliphatic acids; natural fatsand the like. In other words, all the solvents conventionally used foretching magnesium, zinc and alloys thereof in making printing plates canbe used in the present invention. As representative of the commerciallyavailable aromatic liquids which can also be utilized, there are PenolaH.A.N. (trade nan1e) and hellSol 71 (trade name of The ShellInternational Petroleum Co., Ltd.). When the metal plate mainlyconsisting of aluminum is treated with the etching bath having thedesired composition containing the aforesaid organic liquid, a largeamount of heat is generated, and thus a liquid having a low boilingpoint tends to be evaporated during the operation. This will change thecomposition of the etching bath. However, when one of the preferredorganic liquids of this invention, having a boiling point higher thanC., is employed, the life of the etching bath is prolonged. Also, it isa necessary condition that the organic liquid be in a liquid state atthe etching temperature and that the organic liquid be chemicallystable. The organic liquids described above can be used alone or asmixtures thereof. The amount of the organic liquid which is added isusually about l-l0 percent by volume, preferably about 2-5 percent basedon the volume of the etching bath.

From the above description, it is clear that any water-immiscibleorganic solvents can be employed in this invention ifthey will form afilm on the surface of an aluminum base metal or an aluminum base alloyto thereby provide acid resistance to the surface.

For use in the invention, the organic solvents must satisfy a fewconditions. First, they must be liquid in the etching process, and theymust not be dissolved in the etching bath, this being implied by theexpression water-immiscible. It should be noted that the termwater-immiscible is not, strictly speaking, entirely correct, since someorganic solvents which are utilized can be immiscible with water but maybe dissolved in an aqueous solution of the sulfuric acid as utilized inthe present invention. However, the basic requirements are that theorganic solvents retain their liquid state, do not lead todecomposition, have an acid protective power" and maintain the acidprotective power" during processing. In general, it is to be understoodthat water-immiscible solvents satisfy the aforesaid requirements.

The reason for adding the water-immiscible organic liquid to the etchingbath will be described below, together with an explanation of the actionof the surface active agent during etching.

First, the surface active agent to be incorporated into the etching pathand the etchant liquid of this invention will be explained in greaterdetail.

The surface active agent employed in this invention is one prepared bythe phosphoric-esteriflcation of an alkylene oxide condensed typenonionic surface active agent, which may be in the form of a free acid,a neutralized salt, or an additive, such as a salt of Na, K, Li or thelike, or an amine salt. The surface active agent of the presentinvention may be used in combination with other surface active agents.

As the alkylene oxide employed in the surface active agent used in thisinvention, there is preferably employed a lower alkylene oxide, such asethylene oxide or propylene oxide. The alkylene oxide may be used as aform ofa single condensate or a mixed condensate.

Typical examples of the aforesaid surface active agent are shown by thefollowing general formulas:

(ill) (CHKEHO) and (CH CH O) may occupy any desired posltlon.

position.

Some types of surface active agents represented by the aforesaid generalformulas cannot be prepared as a pure form of compound but are usuallyobtained as a mixture, and this mixture may be effectively added to theetchant liquid as a mixture, with comparable results to the case ofadding the surface active agent in pure fon'n. in addition, the numberof ethylene oxide or propylene oxide units (the number shown by a,b,---, l in the above formula) added during the preparation of thesurface active agents depends on the kind and concentration of thewater-immiscible organic liquid, and the type of oleophilic group in thephosphoric acid ester. In general, it is preferable that the groups beadded so as to provide a suitable HLB value to emulsify the organicsolvent, e.g., a HLB value of 8-18.

To further amplify upon the above paragraph, when producing an ethyleneoxide addition product or a propylene oxide addition product, theaverage addition number to the groups is shown by the general formula RO (the aliphatic alcohol group). This number may be known, but thecomposition of the polyoxyethylene alkyl ethers obtained show adistribution with respect to the number of ethylene oxide groups presentwhen they are esterified with phosphoric acid. Accordingly, it is verydifficult to obtain the pure monoester, diester, or triester. In thepresent invention, mixtures of these esterscan be effectively employed,and, as indicated, a highly purified form thereof is not alwaysrequired.

Further, as recited, the number of the ethylene oxide or propylene oxideunits (a, b, c, l) are selected so that the resultant phosphoric esterhas the required HLB value. The ethylene oxide-HLB relationship isfairly significant, but the propylene oxide-HLB relationship is somewhatlessened. The number of units utilized can be easily selected accordingto the type and the amount (concentration) of the water-immiscibleorganic liquid utilized, the general theories involved being well knownin the field of surface active agents.

Further, note that the number of oleophilic groups is one in generalformula (1), two in general formula (2) and three in general formula(3). This illustrates that mixtures of the above may be utilized, sinceHLB illustrates an additive effect. Of course, it is always necessary toconsider the emulsifying action of the organic liquid involved.

The carbon number of R in the formula must be greater than 4, preferablyfrom -20, and the number of propylene oxide and ethylene oxide groups isusually 1-40, preferably 3-20. The hydrophilic property of the surfaceactive agent will be increased as the number of these groups increases.The phosphoric acid ester is stable in the etchant liquid of thisinvention and has the property of absorbing on the surface of theaforesaid metals having a high hydrophilic property more inpreferentially than the corrosive components in the etching bath.

The amount of the aforesaid surface active agent which is added is about0.05-about 8 percent by weight, preferably about 0.1-about 1 percent byweight, based on the total weight of the etching bath. If the amount ofthe surface active agent is less than about'0.05 percent by weight, theanticorrosion film becomes weak, which causes side etching(undercutting) of the relief. if the amount of the surface active agentis larger than about 8 percent by weight the anticorrosion film becomestoo strong to allow the etching to proceed effectively, and hence therelief does not obtain a vertical configuration but develops an inclinedetching pattern, which is generally unacceptable.

it is believed that the actions of the water-immiscible organic liquidand the surface active agent in the etching bath of this invention areas follows:

The surface active agent will emulsify the aforesaid waterimmiscibleorganic liquid in the etching bath by stirring the bath, and when theetching bath containing the surface active agent splashes or flows alongthe surface of the plate of a metal mainly consisting of aluminum, theemulsion will be destroyed and the hydrophilic group of the surfaceactive agent will be absorbed on the surface of the aforesaid metalplate while the oleophilic group thereof will be combined with theorganic liquid, thereby forming a corrosion-resistant film oforganicliquid on the surface of the aforesaid metal. In other words, when theetching bath of this invention is splashed onto the surface of themetallic plate having the photographic image of an acid-resistantcoating which is subjected to an acid-resistant coating treatment, theetching proceeds, leaving the acid-resistant coating portions intact.Further, the etched portions will always be covered by the aforesaidanticorrosion film. The film is broken" by the mechanical action, suchas the splashing action of etching bath which is further splashed ontothe plate, thereby causing etching by means of the etching componentstherein. However, since the action of the etching components which reachthe relief by breaking" the anticorrosion film of the relief, will beweak in comparison to the action thereof on the portions excluding therelief, which is covered by the anticorrosion film, side etching of therelief will be prevented, thereby achieving etching in accordance withthe present invention.

To further amplify on the above, the emulsion of the etching liquid isdestroyed on the surface of the metal to form an anticorrosion film ofthe surface active agent and the organic liquid. This film is fairlyweak, and hence when the etching bath splashes upon the film, the filmwill be removed and fresh etching component will reach the metal surfaceto etch the metal. in this case, since the impact force of the etchingbath which is splashed up to the film on the relief side is weaker thanthe impact force thereof splashed onto a flat surface of the plate, theproportion of the film removed at the side of the relief will belessened, and hence the relief area will be etched to a lesser extentthan other portions of the plate. See Example 1.

in addition, according to the third and fourth embodiments of thepresent invention, there is provided a process wherein the surface of ametal mainly consisting of aluminum having thereon a photographic image(which has been subjected to an acid resistant coating treatment) isetched with either the aforesaid etchant liquid or the etching bath ofthe present invention. That is, the metal is etched by splashing thereonthe etchant liquid consisting of an aqueous sulfuric acid solutioncontaining the ions of at least one halogen and the ions of at least onemetal having an ionization tendency less than that of aluminum; theetchant liquid may also further contain No therein.

To conduct the etching process of this invention more effectively, theetchant liquid is charged into the tank of an etching machine and theetchant liquid is splashed upon a flat or cylindrical plate of the metalmainly consisting of aluminum having thereon, for instance, a halftonephotographic image which has been subjected to an acid resistant coatingtreatment, or a light sensitive coating on the surface of the metal canbe exposed to light through a negative having an image therein,developed to form an image and (usually) further hardened so that theunexposed areas of the composite image will be etched while the acidresistant coating produces the image areas of the metal plate. Theprocess can comprise rotating the splash paddle of the etching machineflow etchant over the plate. The apparatus described is well known tothose skilled in the art.

In still another embodiment of the process of this invention there isprovided an etching process wherein the etching of the metallic platemade of metal mainly consisting of aluminum is conducted by using theetching bath of this invention. ln this embodiment of the process ofthis invention, the surface of a metallic plate made of metal mainlyconsisting of aluminum having thereon a photographic image which hasbeen subjected to an acid resistant coating treatment is etched by theetching bath consisting of an aqueous sulfuric acid solution containingthe ions of at least one halogen, the ions of at least one metal havingan ionization tendency less than that of aluminum, a watebimmiscibleorganic liquid and a surface active agent prepared by thephosphoric-esterification of a condensed type nonionic surface activeagent of alkylene oxide, or (another embodiment) the etching bath mayfurther contain N To perform the etching process of this invention moreeffec tively, the etching bath composition of this invention isemulsified by stirring it in a tank of an etching machine. Thereafter,the emulsified etching bath is applied to the surface of a flat orcylindrical metallic plate made of metal mainly consisting of aluminumhaving thereon a line, a character, or halftone photographic image whichhas been subjected to an acid resistant coating treatment by rotatingthe splash paddle of the etching machine. This etching process can beconducted in almost the same manner as the well-known powderless"etching process.

The extent of the side etch" can be shown by the etch factor, which isthe numerical value obtained by dividing the depth of etching byone-half of the reduced width of the acid resistant coating. Etching isbetter as this value is larger. In this specification, the etch factoris employed as a means for determining the extent of etching.

The practical application of the present invention will now be explainedwith reference to the following examples.

EXAMPLE 1 Into an etching tank equipped with a stirrer and a splashingpaddle for splashing an etchant liquid onto the surface of a metallicplate having thereon a photographic image of an acidresistant coating,there was charged a mixture of the following components to provide anetchant liquid:

A flat plate of an alloy consisting of 1.1 percent by weight Zn,unavoidable impurities, balance A1, x20 sq. cm. in area, having thereona halftone image of 6.5 line/sq. inch consisting of an acid-resistantcoating, was mounted on an etching machine, the resist face of the platefacing the etching tank containing the etchant liquid prepared above.The etchant liquid was then splashed onto the surface of the metallicplate for about 2 minutes by rotating the splashing paddle while alsorotating the metallic plate and moving it back and forth and fromside-to-side in the tank. A temperature of 30-32 C. was used to providean etched plate. The etched plate was then soaked in water, soaked inaqueous 3 percent by weight NaOH solution, washed with water and dried.

The depth of the deepest portions of the halftone was 0.22 mm., that ofthe shallowest portions thereof was 0.08 mm., and the etched plate couldbe used as a halftone engraving.

When the same procedure as above was repeated employing hydrofluoricacid H percent nickel fluoride 0.41 percent, almost identical resultswere obtained.

EXAMPLE 2 Into the tank of the etching machine employed in example 1,there was charged a mixture of the folllowing components to provide anetchant liquid:

Parts by weight Water Commercial sulfuric acid (98% by weight H 50,s.g., I84) Commercial hydrochloric acid (36% by weight HCl s.g. LIX)Aqueous FcCl solution [42% by weight FeCl s.g. L45) 7.8 liters (85.2%)

0530 litcr 13.2%)

0.210111mo4'se 0.480 li1er 1.2%

A flat plate of alloy consisting of l.4% Zn, 0.4% Sn, unavoidableimpurities, balance Al having thereon the same halftone image as inexample 1 was etched under the same conditions as in example 1 toprovide the etched metallic plate.

The depth of the deepest portions of the halftone was 0.16 mm., that ofthe shallowest portions thereof was 0.08 mm., and the etched metallicplate could be used as a halftone engraving.

EXAMPLE 3 Into an etching tank equipped with a stirrer and a splashingpaddle for splashing an etching bath onto the surface of a plate havingthereon a photographic image which had been subjected to anacid-resistant coating treatment, there was charged a mixture of thefollowing components to provide an etchant liquid:

To the etchant liquid prepared above were added the following componentsto provide an etching bath:

6. Solvesso lSO 7. Na-salt of the phosphoric acid ester ofpolyoxyethylenc lauryl ether (mainly monocstcr) 0.35 liter (4.0% byvol.)

Before starting etching, the etching bath thus prepared was stirred forseveral minutes. A flat plate (l0X20 sq. cm.) of an alloy consisting of3.5 Zn, unavoidable impurities, balance A1, having thereon aphotographic image which had been subjected to an acid resistant coatingtreatment was mounted in the etching machine, the resist face of theplate facing the bottom of the tank. The etching bath was then splashedonto the resist face of the plate for l5 minutes at 303 2 C. by rotatingthe etching paddle of the etching machine while rotating the metallicplate back and forth and form side-to-side. The side of the charactersof the photographic image formed on the metallic plate was 7-8 pointtype, and they illustrated both a thick rule and a fine rule. The etchedplate was washed with water and dried. The etch factor of the etchedspecimen was 40-60.

In addition, when the same procedure as above was repeated employinghydrofluoric acid 0.3 percent and nickel fluoride about 0.4 percentalmost identical results were obtained.

EXAMPLE 4 Parts by weight Water Commercial sulfuric acid (98% by weightH,SO s.g., L84) Commercial hydrochloric acid (36% by weight of HCl s.g.,L18) CuCl,.2H,0

8 liters (871%) 0.52s liter 10.0%

0.240 liter l 1%)- To the etchant liquid prepared above were added thefollowing components to provide an etching bath:

5. Diethylbenzcne 6. Phosphoric acid ester of polyoxyethylenenonylphenyl ether (mixture of monoester and diester) 0.35 liter (4.0% byvol.)

A flat plate of an aluminum alloy consisting of l.l% Zn, unavoidableimpurities, balance Al (lX20 sq. cm.) having thereon a photographicimage of an acid-resistant coating was mounted on the etching machinewith the resist facing the bottom. After emulsifying the etching bath,the etching bath was splashed onto the resist face for IS minutes at3032 C., by rotating the splashing paddle of the etching machine. Theetched plate was soaked in an aqueous 3 percent by weight NaOH solution,washed with water and dried. The average depth of the etch was 0.35 mm.andthe etch factor was about 30.

EXAMPLE 5 Parts by weight Water Commercial sulfuric acid (98% by weight",SO,

. Commercial hydrochloric acid Commercial nitric acid (63% by weight HNOs.g., L38) 8 liters (86.7%)

0.528 liter (100%) 0.240 nmume 0.056 liter (0.5%)

To the etchant liquid prepared above, the following compositions wereadded to provide an etching bath:

6. Solvesso I50 0.353 liter (4.0% by vol.) 7. Phosphoric acid ester ofpolyoxyethylene nonylphenyl) ether (mixture of monoestcr and diester)28.7 g. (030%) A flat plate of an aluminum alloy consisting of l.l% Zn,unavoidable impurities, balance Al (area 10x20 sq. cm.) having thereon aphotographic image as, in example 4 was mounted on the etching machinewith the resist face facing the bottom of the tank. After emulsifyingthe etching bath, the etching bath was splashed onto the resist face forl0 minutes at 3033 C. by rotating the splashing paddle to conductetching. The etched plate was soaked in a caustic soda aqueous solutionof 3 percent by weight NaOH washed with water and dried. The depth ofthe deepest portion of the etched portions was about 0. l 45 mm. and theetch factor was about 30.

EXAMPLE 6 Parts by weight 7.5 liters (847%) Water Commercial sulfuricacid (98% by weight l"l,SO s.g., L84 .Cnmmercial hydrochloric acid (36%by weight HCl sg, l.ltl) .Commcrcial nitric acid (63% by weight HNOs.gr, L38) Aqueous FcCl solution (45% by weight FcCL s.g., L45) 0.528liter (9.8%)

0.480 liter (2.2%),

0.ll2 liter L011) 0.432 liter (2.l'b)

To the etchant liquid prepared above were added the following componentsto provide an etching bath:

6. Penola H.A.N.

7. Phosphoric acid ester of polyoxyethylcnc nonylphcnyl ether (monoesterand diester) 0.302 liter (3.4% by vol.

A flat metallic plate as in example 4 was mounted on'the etchingmachine, facing the resist face thereof to the bottom, and afteremulsifying the etching bath prepared above, the etching bath wassplashed onto the resist face of the plate for 10 minutes at 2933 C. Theetched plate was soaked in an aqueous 3 percent by weight NaOH solution,washed with water and dried. The depth of the deepest portion of etchwas about 40 mm. and the etch factor was about l5.

3. Commercial hydro- EXAM P LE 7 Continued Table- Continued chloric acid0144 liter 0.7% (36% by weight HCl (36% by weight ac] 5. ms s.g., l.l8)4. Commercial nitric acid 0.056 liter (0.5%) 4. ciici,.6it,o 140 g. 0.8%5 03% by weight HNO, 5. CuCl, so 0.7% 5 ms s.cuc|,.2|i,o 232 2.0%

To the etchant liquid were added the following components to provide anetching bath; To the etchant liquid prepared above were added thefollowing components to provide an etching bath:

6. Solvesso I50 302 g. (3.5% by vol.) 7. Phosphoric acid ester 6.Diisopropyl benzene 0.350 liter (4.0% by vol.)

of polyoxyethylcne 7. Phosphoric acid ester 7 nonylphenyl) ether ofpolyoxycthylene (mainly diester) 23.2 g. (0.25%) nonylphcnyl ether 28.4(0.30%)

A flat plate of an aluminum alloy consisting of 2.0% Zn, A g 8 3. 2" g 9a unavoidable impurities, balance Al, having thereon a photounfvm e 'f fa g i 8 graphic image of an acid-resistant coating as in example 4 wasif? as i i s a t 'P etched for 10 minutes at 26-30 C. The metallic platethus i t mg "2 etched was soaked in a diluted caustic soda aqueoussolution E e F as 522 6 8 (4 percent by weight NaOH), washed with waterand dried. t i f E i or ggz g g f The average depth of the etch was 0.40mm. and the etch fac- SP g pd e at a rage o 6 etc 8 p ale tor was about40 soaked in an aqueous 3 percent by welght NaOH solution,

washed with water and dried. The depth of the deepest etch EXAMPLE 8portion was about 0.45 mm. and the etch factor was 30-45.

30 EXAMPLE 10 P' rt. b w-i ht d g y L g Into the tank of the etchmgmachmc employed in example 3 there was charged a mixture of thefollowing component to l. Water 8 liters (86.2%) i h .d 2. Commercialsulfuric p 6 etc ant q acid 0.630 liter 12.0%) (98% by weight H1804 5.L84) NiCl,.6H,0 180 g. |.0% 1. Water 1.5 liters ssssa 4. Cu(NO ),.3H O90 g. (0.8%). 2. Commercial sulfuric acid 0.590 liter [0.0%]

(98% by Weight mm. $.g. 1.84) 3. Commercial hydrochloric To the etchantllquld thus prepared were added the followacid 0.495 liter 2.0% ingcomposition to provide an etching bath: Weigh s.g. l. 4. Commercialnitric acid (H25 liter l.0%)

(63% by weight HNO; 5 Sh -|1'r 1| -01 L e uh l I 5. Aqueous FeClsulution 0.473 liter (2.7%)

(trade name of Shell c International Petrol- (42 b by Weigh FLC I sag.L45) cum Co.) 0.396 liter (4.6% by vol.) 6. Na-salt ol'the phosphoric('U(NO)"'H*O (05%) acid ester of polynxy- 5 ethylene lauryl ether (mm'y(032%) To the etchant liquid prepared above were added the followingcomponents to provide an etching bath:

A flat plate of an aluminum alloy consisting of 1.0% Zn, 0.5% Sn,unavoidable impurities, balance Al, having thereon t a photographicimage of an acid resistant coating as in exam- 18mm" by o o 8.Phosphorlc acid ester pie 4 was etched by the etching bath for 15minutes at 25 -27 of pmymymhymc C. The metallic plate thus etched wassoaked in an aqueous (3 nonylphenyl ether 43.0 g. 0.25% percent byweight) NaOH solution, washed with water and dried. The average depth ofthe etch was 0.55 mm. and the etch fa r w a u 4 A flat plate of analuminum alloy consisting of 1.3% Zn and unavoidable impurities (havingan area of 12X22 sq. cm.) hav' EXAMPLE 9 ing thereon a photographicimage of an acid-resistant coating, lnto the tank of the etching machineemployed in example 3 the Images of whlch were characiefs of 6 P l YPwas there was charged a mixture of the following components to mountedthe t g machlhe facing the f"? the provide an etcham liquid; bottom.After emulsifying the etching bath with stirring. the plate was etchedfor 10 minutes at 3335 by rotating the splashing paddle at a rate of 390rpm. The etched plate was soaked in an aqueous 3 percent by weight NaOHsolution, Pam by washed with water, and dried. The depth of the deepestetch portion was about 0.40 mm. and the etch factor was 35. 1. Water 8liters (86.9%) 2. Commercial sulfuric EXAMPLE 1 1 acid 0.52s liter (98%]a 75 lnto the tank of the etching machine employed in example 3 s. 3Commercial hydro there was charged a m xture of the following componentsto chloric acid 0.13s liter 0.3% provide an etchant liquid:

Parts by weight 0.680 liter (13.9%)

0.07 liter 0.3% 170 g. 1.0% 105 g. 0.9%

To the etchant liquid prepared above were added the following componentsto provide an etching bath:

6. Solvesso 150 0.305 liter (3.4%

by volume) 7. Compound prepared by phosphoric esterilication of anequimolar mixture of polyoxycthylene nonylphenyl ether and laurylalcohol A flat plate (12x20 sq. cm. in area) of an aluminum alloyconsisting of 1.0% Zn, 0.1% Sn, unavoidable impurities, balance Al,having thereon a photographic image of a resist as in example 10, wasmounted on the etching machine facing the resist face towards theetching tank. After emulsifying the etching bath by stirring, the platewas etched with the etching bath at 30-32 C. for 10 minutes by splashingit onto the surface of the plate by rotating the splashing paddle of theetching machine. The etched plate was soaked in an aqueous 3 percent byweight NaOH solution, washed with water and dried. The depth of thedeepest etch was 0.60 mm. and the average etch factor was 30.

EXAMPLE l2 Parts by weight 1. Water 2. Commercial sulfuric acid (98% byweight l'l,SO s.g. 1.84)

3. Commercial hydrochloric acid (36% by weight HCI, 8.5.

7.8 liters (85.3%)

0.530 liter (10.0%)

Ollfllhcr (0.9%) 4. Aqueous FcCl, solution 0.480 liter (3.0%)

5. Cu(NO,),3H,0 100 g. 0.5%

To the etchant liquid prepared above were added the following componentsto provide an etching bath:

0.275 liter (3.0% by volume) 6. Solvesso 100 7. Compound prepared by thephosphoric esteril'ication of a mixture of a synthetic alcohol having12- carbon and polyoxyethylene alltyl ether of the alcohol added withethylene oxide A flat plate (10X20 sq. cm. in area) consisting of 99.4percent and unavoidable impurities, having thereon a photographic imageof a resist consisting of 5 point style characters, was mounted on theetching machine facing the resist face towards the etching tank. Afteremulsifying the etching bath in the tank with stirring, the plate wasetched by splashing the etching bath onto the resist face of the platefor 10 minutes. The etched plate was soaked in an aqueous 3 percent byweight NaOH solution, washed with water and dried. The depth of thedeepest etch was 0.3 mm. and the average etch factor was 35.

EXAMPLE l3 Into the tank of the etching machine employed in example 3there was charged a mixture of the following components:

Parts by weight acid (36% by weight HCl, s.g.

0.530 liter l0.0%

1.18) 0.067 liter 0.3% 4. NiCl,-6H,0 360 g. 2.0% 5.CuC1,2H,0 97 g.(0.8%)

To the etchant liquid thus prepared were added the following componentsto provide an etching bath:

0345 litcr (4.0% by volume) 28.5 g. 0.30%

6. Kerosene 7. Phosphoric acid ester of polyoxyethylenc alkyl etherprepared by adding 3 moles of propylene oxide and 5 moles of ethyleneoxide to 1 mole of lauryl alcohol A flat plate (10x22 sq. cm. in area)of an aluminum alloy consisting of 1.1% Zn, unavoidable impurities,balance Al, having thereon a photographic image of resist (the imagesbeing 6 point style characters with a fine rule and a fine wave rule)was mounted on the etching machine facing the resist face to the bottom.After emulsifying the etching bath by stirring, the plate was etched bythe etching bath by splashing the etching bath onto the resist face for10 minutes. The etched plate was soaked in an aqueous 3 percent byweight NaOH solution, washed with water and dried. The depth of thedeepest etch was 0.50 mm. and the average etch factor was In addition,an etching bath having the same composition as above with the exceptionthat Shell Vitrea Oil 13 was used instead of kerosene was used toperform an etch in the same manner. The results were almost identical tothose above, and the average etch factor was 30.

EXAMPLE 14 lnto the tank of the etching machine employed in example 3there was charged a mixture of the following components to provide anetchant liquid:

Parts by weight 1. Water 8 liters (86.5%) 2. Commercial sulfuric acid(98% by weight H,S0,, s.g.

1.84) 0.585 liter (11.0%) 3. NiCl,-6H,0 260 g. (1.5%) 4. CuCl,'2H,0 128g. (1.0%)

To the etchant liquid prepared above were added the following componentsto provide an etching bath:

EXAMPLE l6 Into the tank of the etching machine employed in example 3,there was charged a mixture of the following components to 5 provide anetchant liquid:

5. Solvesso I50 0.3 liter 2.5% by volume) Parts by weight 6. Compoundsprepared by the phosphoric esterification of an equimolar mixmm of 1.Water 8 liters (88.2%) l o h l alky] Ether 2. Commercial sulfuric acidobtained by adding 3 moles of (98% y Weight "1504- 4;- propylene oxideand 8 moles of 0.48 liter (9.2%] ethylene id to 1 mole f 3. Commercialhydrochloric acid lauryl alcohol and polyoxyethylene y wflighl laurylether obtained by adding -8- 014 NIH-1%) 8 moles of ethylene oxide to lz' '80 B- (L195) mole of lauryl alcohol 33 g. 0.35% I QM Q 36 g A flatplate (10x22 sq. cm. in area) of an aluminum alloy T0 the etchant liquidprepared above were added the folconsisting of 3.2 percent Cu, 0.25% Mg,unavoidable impurilowing p n nts t Provide n t hing balhl ties, balanceAl, having thereon a photographic image of a resist as in example l3,was mounted on the etching machine facing the resist face to the bottom.After emulsifying the rsolvcsfl, m0 0 32mcr(3 6% by etching bathprepared above with stirring, the plate was volume) etched withsplashing the etching bath onto the resist fact of P acid the plate for10 minutes. The etched plate was soaked in an polymycmylcnc ether 21.6g. (polyoxyethylcne aqueous 3 percent by weight NaOH solution, washedwith waterand dried. The depth of the deepest etch was 0.35 mm. and theavera e etch factor was 40.

g A flat plate (10x20 sq. cm. In area) of an aluminum alloy EXAMPLE 5consisting of 1.3% Zn, 0.2% Sn, unavoidable impurities, i balance Al,having thereon a halftone photographic image or [mo a of an etchingmachme f' a Surfer resist, said image being 7-8 point style characterswith a fine i Splashmg paddle was charged flmlxture of the rule, wasmounted on the etching machine facing the resist owing components toprovide an etchant liquid. face to the bottom. The plate was then etchedby splashing the etching bath onto the resist face by rotating thesplashing paddle at 440 rpm. for 10 minutes at 26-27 C. The etched plateParts by weight 40 was soaked in a caustic soda aqueous solution of 3percent by weight NaOH, washed with water and dried. The depth of the 1.Water 40 m (310%) etch was 0.40 mm. in average. 2. Commercial sulfuricacid When the same procedure as above was repeated employing :32 by 2 64mm) 8%) Xylene instead of Solvesso 100, substantially identical results3. Commercial hydrochloric acid were obtamed'.

(36% by weight HCI, As a final point, with respect to the use of theexpression uismm (13%) 13%) navoidable in describing the aluminum of thepresent inven- 382 (043%) tion, this term is utilized because it isimpossible, in practice, 5. cuci zmo 286 g. 0.47%

to easily produce an alumina having a purity of 100 percent. 50Accordingly, commercially available high purity aluminum To the etchantliquid prepared above were added the foL conta ns, as a matter of coursea very small amount ofimpuril ties. Since the removal of such impuritiesIS very difficult from owing components to provide an etching bath: u

a commercial viewpoint, the term unavoidable has been utilized to definesuch aluminum. We claim: Suit/c550 150 L13 liters y 1. An etchingprocess which comprises splashing an etchant Phosphoric acid ester ofmum) liquid upon the surface of a metallic plate, said platecomprispolyoxyelhylenemdccyl 135 (018%) ing a metal consistingessentially of aluminum, and having ether thereon a photographic imageformed of an acid resistant coating, said etchant liquid comprising anaqueous sulfuric acid solution containing the ions of at least onehalogen and the ions of at least one metal having an ionization tendencyA flat plate (27x42 sq. cm. in area) of an aluminum alloy less than thatof aluminum, said etchant liquid containing the consisting of 1.5% Zn,unavoidable impurities, balance Al, sulfuric acid in an amount of fromabout 3 to about 20 percent having a photographic image of a resist, theimage of which by weight, said metal ions in an amount of from about0.004 to was 68 point style characters with a thick rule and a finerule, about 2.0 gram-ions/liter, and said halogen ions in an amount wasmounted on the etching machine. After emulsifying the of from about 0.1to about 7.0 grams-ions/liter. etching bath by rotating the stirrer, theplate was etched by 2. The etching process of claim 1 wherein theetchant liquid splashing the etching bath onto the resist face at 3 l-35C. for further comprises N0 1 in an amount less than about 2 gram- 7minutes by rotating the splashing paddle at a rate of 580 ions/liter.rpm. The etched plate was then soaked in an aqueous 3 per- 3. Theetching process of claim 1 wherein said metal is an cent by weight NaOHsolution, washed with water and dried. aluminum alloy consistingessentially of about 0.5 to about 10 The average depth of etch was 0.55mm. and the average etch percent by weight Zn and a small amount ofimpurities, the factor was 50. balance being aluminum.

4. The etching process of claim 1 wherein said metal is an aluminumalloy consisting essentially of about 0.5 to about percent by weight Zn,about 0.04 to about 2.0 percent by weight Sn and a small amount ofimpurities, the balance being aluminum.

5. An etching process which comprises splashing an'etching bath upon thesurface of a metallic plate, said plate comprising a metal consistingessentially of aluminum and having thereon a photographic image of anacid-resistant coating, said etching bath comprising at least onehalogen ion present in a concentration of from about 0.1 to about 7.0grams-ions/liter, from about 0.004 to about 2.0 gram-ions/liter of theions of a metal having an ionization tendency less than that ofaluminum, from about 1 percent to about 10 percent by volume of awater-immiscible organic liquid, from about 0.05 percent to about 8percent by weight of a surface active agent prepared by thephosphoric-esterification of a condensation-type 7. The etching processof claim 5 wherein said metal is an aluminum alloy consistingessentially of about 0.5 to about l0 percent by weight Zn, about 0.04 toabout 2.0 percent by weight Sn and a small amount ofimpurities, thebalance being aluminum.

8. The etching process of claim 5 wherein said metal is an aluminumalloy consisting essentially of about 0.5 to about 10 percent by weightZn and a small amount of impurities, the balance being aluminum.

2. The etching process of claim 1 wherein the etchant liquid furthercomprises NO3 in an amount less than about 2 gram-ions/liter.
 3. Theetching process of claim 1 wherein said metal is an aluminum alloyconsisting essentially of about 0.5 to about 10 percent by weight Zn anda small amount of impurities, the balance being aluminum.
 4. The etchingprocess of claim 1 wherein said metal is an aluminum alloy consistingessentially of about 0.5 to about 10 percent by weight Zn, about 0.04 toabout 2.0 percent by weight Sn and a small amount of impurities, thebalance being aluminum.
 5. An etching process which comprises splashingan etching bath upon the surface of a metallic plate, said platecomprising a metal consisting essentially of aluminum and having thereona photographic image of an acid-resistant coating, said etching bathcomprising at least one halogen ion present in a concentration of fromabout 0.1 to about 7.0 grams-ions/liter, from about 0.004 to about 2.0gram-ions/liter of the ions of a metal having an ionization tendencyless than that of aluminum, from about 1 percent to about 10 percent byvolume of a water-immiscible organic liquid, from about 0.05 percent toabout 8 percent by weight of a surface active agent prepared by thephosphoric-esterification of a condensation-type nonionic surface activeagent of an alkylene oxide and from about 3 percent to about 20 percentby weight sulfuric acid, the materials recited being present in anaqueous solution.
 6. The etching process of claim 5 wherein said etchingbath further comprises NO3 in an amount less than about 2gram-ions/liter.
 7. The etching process of claim 5 wherein said metal isan aluminum alloy consisting essentially of about 0.5 to about 10percent by weight Zn, about 0.04 to about 2.0 percent by weight Sn and asmall amount of impurities, the balance being aluminum.
 8. The etchingprocess of claim 5 wherein said metal is an aluminum alloy consistingessentially of about 0.5 to about 10 percent by weight Zn and a smallamount of impurities, the balance being aluminum.